Generally, internal combustion engines, such as multi-cylinder diesel engines, typically include a crankshaft, a camshaft and a rocker arm shaft. The crankshaft is connected with a plurality of piston rods, which in turn are connected with a plurality of corresponding pistons. Reciprocating movement of the pistons within corresponding combustion cylinders causes rotation of the crankshaft.
The crankshaft is typically interconnected with the camshaft via a gear set and thereby rotatably drives the camshaft during operation. The camshaft includes a plurality of cams, with each cam being associated with an inlet valve, and an exhaust valve or a fuel injector valve. More particularly, the rocker arm shaft carries a plurality of rocker arms, with each rocker arm having a roller follower that engages a corresponding cam on the camshaft. Rotation of the camshaft causes oscillatory pivotal movement of the rocker arms around the rocker arm shaft.
The rocker arm shaft is a hollow pipe, and it may be inserted into a plurality of shaft holes formed through the cylinder head. Since fixing caps are threaded into predetermined shaft holes formed at positions adjacent to both ends of the cylinder head, the rocker arm shaft is rigidly fixed to the shaft hole, respectively.
A problem with a conventional rocker arm shaft for the automobile as described above is that the length of the rocker arm shaft may be changed due to thermal expansion. In other words, if a heat is generated during operation of the automobile engine, it is transmitted to the cylinder head, which in turn is transmitted to the rocker arm shaft and thereby the length of the rocker arm shaft is changed. Due to this, the rocker arm shaft may be twisted or be bent within the shaft holes formed at the positions adjacent to the cylinder head. Alternatively, the cylinder head is broken down due to the thermal expansion of the rocker arm shaft, since the rocker arm shaft is fixed in the shaft hole by means of the fixing cap. If thermal expansion of the rocker arm shaft proceeds continuously, both ends of the rocker arm push the fixing caps and thereby the fixing caps may be forcibly released from the shaft holes.